Addressable Color Changeable LED Structure
There are several ways to construct a color changing light-emitting device package. A number of individual light-emitting diodes (LEDs) of different colors can be placed under a single primary optic. However, this presents difficulties in mixing the colors. If there is no mixing, some primary optics will project the different colors into different directions. When mixing is added, it makes the effective source size larger or compromises the design of the primary optics. The result is that either the beam control is worsened or a larger primary optic is required. These affect the overall performance, form factor, and price of the package.
Alternatively, a number of individual LEDs of different colors can be each placed under its own primary optic. In this case, the beams may not completely overlap, especially at close distances. This can create a color artifact near the border of shadows. Also, this introduces a limitation on the optical design. More than one primary optic is needed and this may not be preferred aesthetically. This is the current solution for color-changing flash modules.
A LED light source based on LED pixels has been discussed for displays, such as a low power addressable LED arrays for color changeable displays. U.S. Pat. No. 9,041,025 discloses LED pixels arranged in groups of four pixels, with the LEDs emitting a single color of light for all pixels. A mold positioned over the LED pixels accepts phosphors for the individual LED pixels in each group. The phosphors in the mold transmit at least three (3) primary colors for respective ones of the LED pixels in each group. A fourth LED pixel in the group can transmit white light.
High Power Addressable LED Structure
A LED light source based on addressable individual or groups of LED pixels that can be turned on or off has been discussed.
A number of individual LEDs can be placed near each other in an array, each under their own primary optic. However, this requires a large number of LEDs and primary optics, and will take a lot of space.
Osram's Micro Advanced Forward-lighting System (μAFS) concept discloses a multi pixel flip chip LED array directly mounted to an active driver integrated circuit (IC). A total of 1024 pixels can be individually addressed through a serial data bus. Several of these units can be integrated in a prototype headlamp to enable advanced light distribution patterns in an evaluation vehicle.
Vehicle manufacturers have realized the advantages of selectively addressable LED arrays for headlights. For example, U.S. Pat. No. 8,314,558 discloses a vehicle headlamp having a plurality of LEDs positioned into an array. The array has at least one row and at least two columns with each LED positioned at an intersection of a row and a column. A LED is illuminated by selectively applying a signal to the row and a signal to the column corresponding to the position of the LED.
High Tunability LEDs with Phosphors Deposited on Wafer
It is difficult to coat different types of phosphors on LED pixels on the same wafer or tile when the LED pixels are in close proximity to each other. Phosphors for one LED pixel may spill over and mix with phosphors of a neighboring LED pixel. Furthermore, light crosstalk between phosphors of neighboring LED pixels varies the color endpoints between packages and reduces the range of color tunability between the color endpoints.
Improved Phosphor Deposition System for LEDs
The use of multi-chip LED fixtures to improve color intermixing has been discussed. For example, Acclaim Lighting describes a color mixing application using a single lens to produce a homogenized beam with blended color and minimal color halos or shadowing. Such multi-chip packages are available from Cree, Osram, Prolight Opto Technology, and Opto Tech Corp.